The production of incandescent lamp filament tungsten filament in tungsten trioxide or blue tungsten oxide needs to be doped with a small amount of potassium oxide, silicon oxide and aluminium oxide, the sum of the three dosages does not exceed 1%, which is the tungsten filament doping process invented by Bartz in 1922. The doped tungsten oxide is reduced to metallic tungsten powder with hydrogen. The reduction process is generally carried out in two steps: the first step at about 630 ℃ to tungsten dioxide (brown tungsten oxide), the second step at about 820 ℃ to tungsten dioxide (brown tungsten oxide).
The second step at about 820 ° C to metallic tungsten powder. The purpose of the two-step reduction is to make the doped potassium give full play to its effect and control the powder size. The doped tungsten powder obtained in this way is then pressed into long, thin square bars in a special mould. The square bar in hydrogen gas, with self-resistance heating (temperature of 3000 ℃ or so) method of sintering, sintered tungsten bar density can reach more than 85% of the theoretical value.
This kind of tungsten bar can be processed into tungsten rod with a diameter of about 3mm by spin forging method, and then further processed into various kinds of tungsten wires with different thicknesses by drawing method of mould. For example, 220V, 15W incandescent lamps with tungsten filament diameter of about 15µ m, and 10,000W tungsten bromine lamps with tungsten filament diameter of about 1.25mm. finer tungsten filaments, such as 220V, 10W incandescent lamps tungsten filament diameter of about 12µ m, it is necessary to use electrolytic corrosion method to produce.
When the diameter of the tungsten filament reaches the micron level, it is difficult to accurately determine its diameter with conventional calipers. Therefore, the international tungsten filament diameter of 0.2mm or less is usually used to cut the length of 200mm filament weight to indicate the thickness of the wire, such as the above 15W incandescent tungsten filament diameter can be used 0.679mg/200mm to indicate.
